Research is currently in three phases on the problem of factors affecting sexual maturation in mammals, and female house mice in particular. First, various factors are being tested in separate experiments to determine how they affect the timing of puberty. Dietary protein levels of 20-40 percent resulted in maturation at 34-35 days of age, whereas higher or lower protein levels produced delays in puberty. Varying the fat and carbohydrate content of the diet between 10 percent and 40 percent of the isocaloric regimen did not affect the timing of maturation. Variations in daylength, male presence or absence and female density have also been shown to affect puberty. The delay of maturation in grouped female mice is effected by a urinary pheromone found in the bladder urine of all female mice, but in excreted urine of only group-caged females. Additional experiments will be conducted on the effects of variations in temperature and humidity on the timing of sexual maturation. These separate tests will be followed by a multi-factor experiment investigating the relative importance of various factors affecting puberty. A final experiment, commencing in the spring of 1976, will involve a long-term assessment of the role of inheritance in the timing of puberty through the use of selective breeding for early and late maturation. BIBILOGRAPHIC REFERENCES: Drickamer, L.C. 1976. Effect of litter size and sex ratio on the sexual maturation of female mice. J. Reprod. Fert. (in press). Drickamer, L.C. Seasonal variation in litter size, body weight and sexual maturation in juvenile female house mice (Mus musculus). Lab. Anim. Care (in press).